A sensor network is an interconnected network of components that sense or measure events in the physical world. These components provide sensor elements that include electric and magnetic field sensors; radio-wave frequency sensors; optical sensors, electro-optic sensors, and infrared sensors; radars; lasers; location/navigation sensors; seismic and pressure-wave sensors; environmental parameter sensors (e.g., wind, humidity, heat); and biochemical, national security-oriented sensors. The detected phenomena are digitized and retained in electronic memory and then upon command transmitted over a wireless network to a central processing system.
The sensor elements are low-cost low-power untethered multifunctional nodes that are connected to a central sink node. Some of these networks are cellular technologies such as narrow-band internet of things (NB-IoT) and a long range wide area network (LoRa/LoRaWAN), and low power wide area networks (LPWAN) such as those constructed by Sigfox of Labège, France. The cellular technologies do not have the needed meshing capability to extend coverage beyond the base station's range. They also have limitations on customizing security features into their communication.
Other networks are internet protocol based structures such as the wireless smart utility network (Wi-SUN), low-rate wireless personal area networks (LR-WPANs), and Zigbee a low-cost, low-power-consumption, two-way, wireless communications standard. The ZigBee standard is a specification for communication in a wireless personal area network (WPAN) for the implementation of the “Internet of things”, as published as the ZigBee Specification, Document 053474r20 Sep. 7, 2012, ZigBee Alliance, Inc. San Ramon, Calif. 94583. Networks such as ZigBee have a stack architecture of which two of the stacks (Media Access Control, and Physical Layer) comply with the IEEE 802.15.4 technical standard (IEEE Standard 802.15.4TM-2011, IEEE, New York, N.Y. 10016-5997 USA, Sep. 5, 2011.
These network structures have mesh functionality, but their radios may not offer the best coverage range compared to their cellular radio counterparts. These IP-based technologies also require either a pre-installation staging process or field configuration. The system setup process can be challenging for electrical technicians and power meter field installation personnel.
FIG. 1A is a diagram of a star-structured network 15 such as used in a network implementing the Zigbee standard. The ZigBee standard provides a simple networking layer and standard application profiles that can be used to create interoperable node elements. In the configuration of FIG. 1a, the star network 15 is formed of fully functional devices FFD and reduced function devices RFD. At least one of the fully functional devices FFD may be designated as a personal area network (PAN) coordinator. The PAN Coordinator FFD-PC is in wireless communication with the gateway device 10 that is in turn in communication with a central computer system 5. In some implementations, the gateway device 10 is integrated within the central computer system 5 and in other implementations, the central computer system 5 is remotely connected through another network protocol such as ethernet or an internet protocol to the gateway device 10.
FIG. 1B is a diagram of a peer-to-peer structured network 30 such as used in a network implementing the Zigbee standard. In the peer-to-peer network 30, each of the fully functional devices FFD is wirelessly in communication with the other fully functional devices FFD. One of the fully functional devices FFD is designated as the PAN coordinator FFD-PC and is in communication with the gateway device 25. In turn, the gateway device 25 is in communication with the central computer system 20, as described above. Any reduced function device RFD connects as a leaf device to one of the fully functional devices FFD because reduced function devices RFD are not allowed to communicate with other fully functional devices FFD.
The ZigBee standard permits other more complex network structures that are known in the art such as a cluster tree network (not shown). The cluster tree network is a special case of the peer-to-peer network 30 in which most devices are fully functional devices FFD. The reduced function devices RFD connect to a cluster tree network as a leaf device at the end of a branch as described above. Any fully functional devices FFD may become a PAN coordinator FFD-PC and provide synchronization services to other fully functional devices FFD or reduced function devices RFD or other PAN Coordinators FFD-PC. Only one of these PAN Coordinators FFD-PC is the overall PAN Coordinators FFD-PC. The overall PAN Coordinators FFD-PC may assume the position as the overall PAN Coordinators FFD-PC because it has greater computational resources than any other device in the PAN.
FIGS. 2A and 2B are a diagram of the message protocol for the physical layer (PHY) protocol data unit (PPDU) and the medium access control (MAC) for the IEEE 802.15.4 technical standard as used in the Zigbee standard. In FIG. 2A, the PPDU structure includes a synchronization header SHR, a physical layer header PHR, and a physical layer payload PSDU. The synchronization header SHR is structured to aid receiver algorithms related to automatic gain control (AGC) settings, antenna diversity selection, timing acquisition, coarse and fine frequency recovery, packet and frame synchronization, channel estimation, and leading edge signal tracking for ranging.
The PHR header conveys information necessary for the successful decoding of the packet by the receiver. The PHR contains information about the data rate used to transmit the PSDU, the duration of the current frame's preamble, and the length of the frame payload. Additionally, six parity check bits are used to further protect the PHR against channel errors.
The PSDU is the physical layer payload and contains the MAC header MHR, the MAC payload, and the MAC footer MFR. The MAC Header MHR is shown in FIG. 2B and contains the frame type; security status; a frame pending field indicating additional data is to follow; an acknowledgement request field that specifies whether an acknowledgment is required from the recipient device on receipt of a data or MAC command frame; a PAN identification compression specifying whether the MAC frame is to be sent containing only one of the PAN identifier fields when both source and destination addresses are present; a destination and source addressing mode; and a frame version.
In applications, where the device nodes of the network are formed by large numbers of sensors where it is impractical to set up a large number of base stations to provide direct wireless coverage, the sensors only need to send small amounts of data intermittently for instance 50-100 bytes every 5 minutes up to once per day, the network structures such as Zigbee and other implementations of the IEEE802.15.4 standard are inefficient and require either a pre-installation staging process or field configuration. The system setup process can be challenging for electrical technicians and power meter field installation personnel.